Adaptive control of backlash in a vehicle powertrain

ABSTRACT

A system and method for controlling backlash in a vehicle powertrain includes the step of controlling a torque request of the powertrain with a first control strategy after an occurrence of a backlash predictor and prior to an occurrence of backlash. The first control strategy is modified when backlash occurs during the first control strategy. The torque request is controlled with the modified first control strategy after another occurrence of a backlash predictor and before another occurrence of backlash.

TECHNICAL FIELD

The present disclosure relates to a system and method for adaptivecontrol of backlash in a vehicle powertrain.

BACKGROUND

In an automotive powertrain, fast and smooth transitions of thedriveline's backlash region following a torque increase request can bechallenging because of uncertainties in operational parameters such asinput torque, driveline friction and the size of the backlash, just toname a few. These uncertainties vary from vehicle to vehicle and evenwithin the same vehicle as it ages. As a result, it may be difficult todetermine when the driveline is in the backlash region and when thebacklash region has been traversed. One system for detecting a lash zoneis described in U.S. Pat. No. 9,037,329, issued on 19 May 2015 andentitled Lash Zone Detection in a Hybrid Electric Vehicle, which ishereby incorporated herein by reference.

Other systems and methods may be employed for determining backlash, butin at least some of these, the adjustments that are made to thedriveline torque to control the backlash may result in a lowering of thepre-lash requested torque to decrease the rate that the driveline passesthrough backlash. This decrease in backlash transition rate combinedwith the uncertainties described above may lead to an unacceptably slowtip-in response to achieve a smooth backlash transition. It wouldtherefore be desirable to have a system and method for controllingbacklash in a vehicle powertrain that overcomes at least some of theseissues.

SUMMARY

In at least some embodiments, a method for controlling backlash in avehicle powertrain includes the step of controlling a torque request ofthe powertrain with a first control strategy after an occurrence of abacklash predictor and prior to an occurrence of backlash. The firstcontrol strategy is modified when backlash occurs during the firstcontrol strategy, and the torque request is controlled with the modifiedfirst control strategy after another occurrence of a backlash predictorand before another occurrence of backlash.

In at least some embodiments, a method for controlling backlash in avehicle powertrain includes the step of reducing at least one of aduration or a maximum torque level of a first control strategy forcontrolling a torque request of the powertrain when the first controlstrategy is implemented after an occurrence of a backlash predictor andbefore an occurrence of backlash, and backlash occurs before completionof the first control strategy.

In at least some embodiments, a system for controlling backlash in avehicle powertrain includes a control system, including at least onecontroller. The control system is configured to implement a firstcontrol strategy for a torque request after an occurrence of a backlashpredictor and before occurrence of a backlash. The control system isfurther configured to modify the first control strategy when backlashoccurs during the first control strategy, and implement the modifiedfirst control strategy after another occurrence of a backlash predictorand before another occurrence of backlash.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a hybrid electric vehicleincluding a control system in accordance with embodiments describedherein;

FIGS. 2A and 2B show torque diagrams for the implementation ofembodiments of control systems and methods described herein;

FIG. 3 shows a flowchart illustrating an adaptive control strategy inaccordance with embodiments described herein for controlling backlashduring one time period in the course of the backlash event;

FIGS. 4A and 4B show lookup tables that can be used as part of theadaptive control strategy illustrated in the flowchart in FIG. 3;

FIG. 5 shows a flowchart illustrating an adaptive control strategy inaccordance with embodiments described herein for controlling backlashduring different time period in the course of the backlash event;

FIG. 6 shows a flowchart illustrating an adaptive control strategy inaccordance with embodiments described herein for controlling backlashduring the lash crossing; and

FIG. 7 shows a flowchart illustrating an adaptive control strategy inaccordance with embodiments described herein during a time periodimmediately following completion of backlash.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

FIG. 1 illustrates a schematic diagram of a hybrid vehicle 10 accordingto an embodiment. The vehicle 10 includes an engine 12, and an electricmachine, which, in the embodiment shown in FIG. 1, is a motor generator(M/G) 14, and alternatively may be a traction motor. The M/G 14 isconfigured to transfer torque to the engine 12, to the vehicle wheels16, or both.

The M/G 14 is connected to the engine 12 using a first clutch 18, alsoknown as a disconnect clutch or the upstream clutch. A second clutch 22,also known as a launch clutch or the downstream clutch, connects the M/G14 to a transmission 24, and all of the input torque to the transmission24 flows through the launch clutch 22. Although the clutches 18, 22 aredescribed and illustrated as hydraulic clutches, other types ofclutches, such as electromechanical clutches may also be used.Alternatively, the clutch 22 may be replaced with a torque converterhaving a bypass clutch, as described further below. In differentembodiments, the downstream clutch 22 refers to various coupling devicesfor the vehicle 10 including a traditional clutch, and a torqueconverter having a bypass (lock-out) clutch. This configuration may usean otherwise conventional automatic step-ratio transmission with atorque converter and is sometimes referred to as a modular hybridtransmission configuration.

The engine 12 output shaft is connected to the disconnect clutch 18,which in turn is connected to the input shaft for the M/G 14. The M/G 14output shaft is connected to the launch clutch 22, which in turn isconnected to the transmission 24. The various components of the vehicle10 are positioned sequentially in series with one another. The launchclutch 22 connects the vehicle prime movers to the driveline 26. Asshown in FIG. 1, the driveline includes the transmission 24,differential 28, vehicle wheels 16, and their interconnectingcomponents. For purposes of powertrain control, and in particularcalculating and using driveline twist, the definition of the drivelinemay be extended to include the engine output shaft 25—i.e., thecrankshaft—the input shaft 27 to the M/G 14, and the M/G output shaft29.

In another embodiment of the vehicle 10, the downstream clutch 22 is abypass clutch with a torque converter. The input from the M/G 14 is theimpeller side of the torque converter, and the output from the torqueconverter to the transmission 24 is the turbine side. The torqueconverter 22 transfers torque using its fluid coupling, and torquemultiplication may occur depending on the amount of slip between theimpeller and turbine sides. The bypass or lock-up clutch for the torqueconverter may be selectively engaged to create a mechanical orfrictional connection between the impeller side and the turbine side fordirect torque transfer. The bypass clutch may be slipped and/or openedto control the amount of torque transferred through the torqueconverter. The torque converter may also include a mechanical lockupclutch.

In the vehicle 10, the launch clutch 22 or bypass clutch for the torqueconverter may be locked to increase fuel efficiency, and may be lockedwhen crossing a lash zone during a tip in or tip out event. Thedrivability and control of the effect of lash crossing within thedriveline depends on the control of the powertrain torque from theengine 12 and/or the electric machine 14. M/G 14 torque may becontrolled to a greater accuracy and with a faster response time thanengine 12 torque. During an electric-only mode of operation for thevehicle 10, the M/G 14 torque may be controlled when crossing a lashzone. During a hybrid mode of operation of the vehicle with both theengine 12 and M/G 14 operating, the M/G 14 torque and engine 12 torquemay be controlled together in order to improve drivability of thevehicle 10 and reduce the effect of lash crossing in the driveline.

In the representative embodiment illustrated, the engine 12 is a directinjection engine. Alternatively, the engine 12 may be another type ofengine or prime mover, such as a port injection engine or fuel cell, oruse various fuel sources, such as diesel, biofuel, natural gas,hydrogen, or the like. In some embodiments, the vehicle 10 also includesa starter motor 30 operatively connected to the engine 12, for example,through a belt or gear drive. The starter motor 30 may be used toprovide torque to start the engine 12 without the addition of torquefrom the M/G 14, such as for a cold start or some high speed startingevents.

The M/G 14 is in communication with a battery 32. The battery 32 may bea high voltage battery. The M/G 14 may be configured to charge thebattery 32 in a regeneration mode, for example when vehicle power outputexceeds driver demand, through regenerative braking, or the like. TheM/G 14 may also be placed in a generator configuration to moderate theamount of engine 12 torque provided to the driveline 26. In one examplethe battery 32 is configured to connect to an external electric grid,such as for a plug-in hybrid electric vehicle (PHEV) with the capabilityto recharge the battery from an electric power grid, which suppliesenergy to an electrical outlet at a charging station. A low voltagebattery may also be present to provide power to the starter motor orother vehicle components, or low voltage power may be provided through aDC to DC converter connected to the battery 32.

In some embodiments, the transmission 24 is an automatic transmissionand connected to the drive wheels 16 in a conventional manner, and mayinclude a differential 28. The vehicle 10 is also provided with a pairof non-driven wheels, however, in alternative embodiments, a transfercase and a second differential can be utilized to positively drive allof the vehicle wheels.

The M/G 14 and the clutches 18, 22 may be located within a motorgenerator case 34, which may be incorporated into the transmission 24case, or alternatively, is a separate case within the vehicle 10. Thetransmission 24 has a gear box to provide various gearing ratios for thevehicle 10. The transmission 24 gearbox may include clutches andplanetary gearsets, or other arrangements of clutches and gear trains asare known in the art. In alternative embodiments, the transmission 24 isa continuously variable transmission or automated mechanicaltransmission. The transmission 24 may be an automatic six speedtransmission, other speed automatic transmission, or other gearbox as isknown in the art.

The transmission 24 is controlled using a transmission control unit(TCU) 36 or the like to operate on a shift schedule, such as aproduction shift schedule, that connects and disconnects elements withinthe gear box to control the gear ratio between the transmission outputand transmission input. The gear ratio of the transmission 24 is theideal torque ratio of the transmission 24. The TCU 36 also acts tocontrol the M/G 14, the clutches 18, 22, and any other components withinthe motor generator case 34.

An engine control unit (ECU) 38 is configured to control the operationof the engine 12. A vehicle system controller (VSC) 40 transfers databetween the TCU 36 and ECU 38 and is also in communication with variousvehicle sensors. The control system 42 for the vehicle 10 may includeany number of controllers, and may be integrated into a singlecontroller, or have various modules. Some or all of the controllers maybe connected by a controller area network (CAN) or other system. Thecontrol system 42 may be configured to control operation of the variouscomponents of the transmission 24, the motor generator assembly 34, thestarter motor 30 and the engine 12 under any of a number of differentconditions, including in a way that minimizes or reduces the effect oflash crossing in the driveline 26 and impact on the driver during tip inor tip out events.

Under normal powertrain conditions, that is with nosubsystems/components faulted, the VSC 40 interprets the driver'sdemands—e.g., PRND and acceleration or deceleration demand—and thendetermines the wheel torque command based on the driver demand andpowertrain limits. In addition, the VSC 40 determines when and how muchtorque each power source needs to provide in order to meet the driver'storque demand and to achieve the operating points (torque and speed) ofthe engine 12 and M/G 14.

The vehicle 10 may have speed sensors 44 positioned at various locationsof the powertrain and driveline 26. The speed sensors 44 provideinformation to the control system 42 regarding the rotational speed of ashaft in approximately real time, although there may be some lag due toresponse time, and signal and data processing. In the embodiment shownin FIG. 1, there is a speed sensor 44 that measures the speed of theengine output-shaft 25 (ω_(eng)), the speed of the M/G 14 input shaft 27(ω_(m)), the speed of the transmission input-shaft 46 (ω_(in)), thespeed of the transmission output-shaft 48 (ω_(out)), and the speed ofone or both of the axles connected to the wheels 16 (ω_(final)).

As a part of the control strategy or algorithm for operation of thevehicle 10, the control system 42 may make an engine 12 torque request(τ_(eng)), a M/G 14 torque request (τ_(m)), or both, as shown in FIG. 1.The net transmission input-torque (τ_(in)) is composed of the electricmotor torque and engine torque (τ_(in)=τ_(m)+τ_(eng)), assuming that thedisconnect and launch clutches 18, 22 are locked. Also show in FIG. 1 isthe transmission output-torque (τ_(out)) and the wheel torque(τ_(final)).

In alternative configurations, the clutch 22 may be replaced with atorque converter unit including a torque converter and a lockup clutchor bypass clutch. The torque converter has torque multiplication effectswhen certain rotational speed differentials exist across the torqueconverter. During torque multiplication, the output torque of the torqueconverter is larger than that of the input torque due to torquemultiplication across the torque converter. Torque multiplication existsfor example, when the vehicle 10 is started from rest and the inputshaft to the torque converter begins to rotate, and the output shaftfrom the torque converter is still at rest or has just begun to rotate.

The lockup clutch or bypass clutch is used to lock out the torqueconverter such that the input and output torques for the downstreamtorque transfer device 22 are equal to one another, and the input andoutput rotational speeds for the device 22 are equal to one another. Alocked clutch eliminates slipping and driveline inefficiency across thetorque converter, for example, when the rotational speed ratio acrossthe torque converter is greater than approximately 0.8, and may increasefuel efficiency for the vehicle 10.

Changing torque amounts and/or directions may cause disturbances oroscillation in the driveline 26 associated with lash crossing. Backlashmay occur in a vehicle driveline 26 whenever one of the wheel 16 torqueand power plant 12, 14 torque change direction from the other. Thischange in torque direction may occur with the vehicle 10 operating withboth the disconnect clutch 18 and the launch clutch 22, or lock outclutch for the torque converter, in a locked or engaged position. Forexample, when vehicle 10 is decelerating, the compression braking effectof the engine 12 provides negative torque to the transmission 24 whichis then passed through the differential 28 and then to the wheels 16. Atthis point, the driveline 26 is wrapped in the negative direction. Ifthe driver provides a power request, or tip in, using the acceleratorpedal, the engine 12 torque switches from negative to positive as itbegins to supply torque to propel the vehicle 10 forward. The driveline26 unwraps, as each driveline component changes from transmittingnegative torque to transmitting positive torque. At some point duringthis transition, the driveline 26 passes through a relaxed state withzero torque applied to the wheels 16.

During this zero torque region, gear teeth in the transmission 24 and/ordifferential 28 may not be tightly coupled with their mating gears andthere may be some play in the driveline 26. Play across multiple sets ofgears acts as cumulative. As the engine 12 continues to provide positivetorque, the driveline 26 will wrap in the positive direction. The gearsmay be quickly coupled resulting in a clunk. Also, the axle connectingthe differential 28 to a wheel 16 may twist slightly as a result ofhigher torque on the differential 28 side of the axle compared to thewheel 16 side. The axle may act as a torsional spring to store thisenergy. As the vehicle 10 begins to accelerate, the wheel 16 torquecatches up to the torque at the differential 28, and any energy storedin the axle is released quickly causing an oscillation in the oppositedirection, or backlash. The result of this backlash crossing is a clunkor noise when the gear teeth hit together, and a reduction in wheeltorque when the axle energy is expended. The clunks and oscillations maybe noticed by a driver depending upon their severity. For a drivelinewith multiple gear meshes arranged in series, each gear mesh may have alash zone. The lash in the driveline cascades or progresses through thegear meshes. After a gear mesh is engaged, the subsequent gear meshcrosses through a lash zone as the torque reversal goes through.Backlash may include main gear lash as well as subsequent gears.

The scenario described above can also happen in the opposite direction.In this case, the driver would be providing a power request, such as atip in of the accelerator pedal for vehicle acceleration, and thensuddenly removing the power request by releasing the accelerator pedalthrough a tip out. The driveline 26 goes from being wrapped in thepositive direction to being wrapped in the negative direction, with asimilar torque dip or hole and clunk during the transition. The effectof the backlash crossing due to sudden acceleration is typically morenoticeable than sudden deceleration.

FIG. 2A shows a torque diagram 50 for the implementation of controlsystems and methods associated with embodiments of the inventiondescribed herein. Like other control strategies and methods describedherein, the control strategy and method associated with the torquediagram 50 in FIG. 2A can be used with vehicle powertrains such as thehybrid electric vehicle powertrain illustrated in FIG. 1, or otherhybrid electric, electric, or conventional powertrains. Such powertrainsmay include engines, transmissions and drive wheels, such as the engine12, M/G 14, transmission 24 and drive wheels 16 depicted in FIG. 1, ormay include different components depending on the configuration. Thetimeline shown in FIG. 2A is divided into four different zones. Thefirst two zones cover a time period prior to backlash occurring, zone 3covers the time period during which backlash is occurring, and a zone 4covers the time period after backlash is complete and the powertraintorque-request returns to an unfiltered level.

Turning to FIGS. 2A and 2B an implementation of a control strategy andmethod are illustrated. A more detailed description of a controlstrategy and method associated with the diagrams in FIGS. 2A and 2B isfound in U.S. patent application entitled: System and Method forControlling Backlash in a Vehicle Powertrain, filed concurrently withand having the same assignee as this application, and having attorneydocket number 83667609, which is hereby incorporated herein byreference. The solid line 52 in diagram 50 shows the driver-requestedtorque; while the dashed line 54 shows the filtered torque-request—i.e.,the torque request that is controlled in accordance with at least someembodiments of the present invention. In general, this embodimentprovides a multi-tier torque request level that quickly increases torquewhen a torque request is received—e.g., when a tip-in occurs—reduces thetorque request level in a second zone, and finally reduces it againduring the time that backlash is occurring.

FIG. 2B shows a torque diagram 56 similar to the torque diagram 50 shownin FIG. 2A. The solid line 58 shows the unfiltered driver-requestedtorque, while the dashed line 60 shows the filtered torque-request. Thedifference between the diagrams 50, 56 is that the control strategydescribed by diagram 50 may be advantageously used when a torqueconverter or downstream clutch—see element 22 shown in FIG. 1—is open,or transitions from a locked state to an open state, while the controlstrategy described by diagram 56 may be used when the torque converteror downstream clutch is locked. As shown in the two diagrams 50, 56,both control systems provide a multi-tiered torque request level toaddress the issue of backlash; however, the torque is held generallyconstant—albeit at different levels—in each of the first three zones indiagram 50, while it is ramped up through each of the zones in thecontrol system illustrated in diagram 56.

Turning to FIG. 3, a flowchart 62 illustrates a first control strategyin accordance with at least some embodiments of the present invention.In the discussion of the various methods illustrated in the flowchartsin FIGS. 3-6, it is understood that these methods may be implemented bya control system, such as the control system 42 described above, orother vehicle powertrain control systems in different powertrainconfigurations. The method starts at step 64 and then a determination ismade at decision block 66 as to whether certain “enable conditions” aremet. In general, this is a determination as to whether the backlashcontrol strategy is needed for the particular situation. One way to viewthe “enable conditions” is to consider them met when a “backlashpredictor” has occurred. There are a number of conditions that indicatea backlash is likely to occur, for example, upon tip-in when a drivertorque request is increased, and the current torque level is negative.In this situation, the increase in torque resulting from the tip-in maycause driveline components to engage harshly, leading to an undesirableeffect on the vehicle operator. Other situations in which backlash islikely to occur are described above, and include changes in torquedirection, the engaging or disengaging of various clutches in thedriveline, decreasing vehicle speed and regenerative braking, just toname a few.

If the “enable conditions” are met, the method moves from the decisionblock 66 to step 68 where certain variables are calculated. Inparticular, a number of inputs are used to determine the zone 1 torquelevel, the duration of zone 1, and whether the torque request should beramped or remain constant. The inputs used for these determinations mayinclude such parameters as the driveline temperature, a current gear ofthe transmission, the road grade, and the driver requested torque. Inaddition, the determination of whether or not a ramped torque isdesired—i.e. whether the control strategy will follow the filteredtorque request 54 shown in the diagram 50, or whether it will follow thefiltered torque request 60 shown in diagram 56—will be based on an inputas to whether the torque converter or other downstream clutch is open orlocked. The driveline temperature may be estimated by using a number ofrelated parameters, such as the transmission oil temperature, the reardifferential temperature, and the ambient temperature. The parametersused for the determinations made at step 68 may be entered into a lookuptable accessible by the control system to determine a torque levelcorresponding to the various measured or estimated input parameters.

In the example shown in FIG. 2A, both the filtered torque request 54 andthe unfiltered torque request 52 are negative prior to point 51, whichoccurs before the beginning of zone 1. Therefore, if a tip-in occurs atthis point along the timeline, it may be considered that the enableconditions are met. Here the unfiltered torque request 52 increasesrapidly until it meets the level of torque requested by the tip-in. Incontrast, the filtered torque request 54 increases more slowly until thebeginning of zone 1, indicated by the point 53. In the implementationshown in the diagram 50, the beginning of zone 1 is where the torqueconverter or other downstream clutch begins to open. In contrast, thebeginning of zone 1 in diagram 56 is indicated by the point 53′ and doesnot include the torque converter or other downstream clutch openingbecause the strategy shown in diagram 56 maintains the locked converteror clutch throughout its implementation.

Returning to the flowchart 62 shown in FIG. 3, once the appropriatedeterminations are made, the torque level is applied at the beginning ofzone 1 as shown in step 70. As implemented in the control strategyillustrated in diagram 50, the torque request is quickly raised to alevel indicated by point 55, which is a level that will provide a veryhigh probability—given the uncertainties of certain measured parametersas described above—that the driveline will transition into the backlashregion if the torque is applied for a sufficient duration. In at leastsome embodiments, the torque level indicated by point 55 may be 20Newton meters (Nm), and may be brought to this level as quickly aspossible without introducing an undesirable driveline disturbance, andwhile ensuring that the filtered torque request does not exceed theunfiltered torque request.

As described above, the torque level may be retrieved from a lookuptable after the input parameters are known. The lookup table may havetorque level values determined based on desired goals for controllingthe backlash. The filtered torque request level for zone 1—e.g., thevalues used in a lookup table—may be obtained by determining the maximumrequested torque that can be applied to quickly unwind the driveline andget near to the start of lash, without producing a “torque hole” feelwhen the torque is dropped to the zone 2 torque, and without allowingthe torque request to be too low so as to cause a delay in the torqueresponse. This maximum requested torque may be determined, for example,from empirical data, theoretical models, or some combination.

In the control strategy illustrated in the diagram 50, the torquerequest level is held constant for the remainder of zone 1; whereas, inthe strategy illustrated in the diagram 56, the torque request levelincreases throughout the duration of zone 1. Initially, there may be asteep increase in the torque request to the point 55′, although it isstill at a lower torque request level than the torque request levelindicated by point 55. As described above, the torque request level maybe controlled to increase throughout zone 1 when the converter or otherdownstream clutch is locked. As shown in the diagram 56, the filteredtorque request strategy 60 continues to increase throughout theremainder of zone 1 until it reaches a maximum at point 57′. The rate ofincrease in the torque request shown in the diagram 56 may be determinedby any method effective to achieve the desired torque request control.In at least some embodiments, this determination may be made based inpart by the torque delivery uncertainty of the engine, the motor, orboth. If, for example, the torque uncertainty is determined to be +/−10Nm, then the torque rate would be in the range of the entireuncertainty, which is 20 Nm over the entire lash crossing event. If thedesired lash crossing event was, for example, 100 milliseconds (ms),then the torque rate would be selected to be in the range between 0 and200 Nm/s.

The next step in the flowchart 62 shown in FIG. 3 is a determinationmade at decision block 72 as to whether the duration of zone 1 has beenexceeded—i.e., whether or not its planned duration is complete. If theduration is complete, the method moves onto the zone 2 control labeled“A” in FIG. 3 and described in detail in conjunction with FIG. 5. If itis determined at decision block 72 that the duration of the zone 1control strategy is not complete, the method moves to step 74 where adecision is made as to whether certain “adaption enable conditions” aremet. These may include for example, an analysis of wheels speeds,whether the transmission is in a gear change, or other parameters thatwould affect the reliability of the information regarding the powertrainbeing in the lash zone—e.g., the quality of the twist speed and angleinformation. The twist speed is the speed of twisting of the driveline,which can be determined, for example, from the difference between thedriveline input speed—i.e., the engine crankshaft speed—to the drivelinespeed at the wheels. A similar determination can be made regarding thetwist angle of the driveline.

If the determination at decision block 74 is made that the enableconditions are met—which would indicate that the information regardingthe lash zone traversal was highly reliable—the strategy moves todecision block 76 where it is determined whether the powertrain is stillin the lash zone or whether lash is complete. If the answer to both ofthese is no, the method loops back to step 70 where the zone one torquelevel and potentially ramp level are applied. If it is determined atdecision block 76 that the powertrain is either in the lash zone or hasalready completely traversed the lash zone and lash is complete, themethod moves to step 78, which is described in more detail below. If thedetermination at decision block 74 is made that the enable conditionsare not met, the strategy moves to step 80, where the determination isstill made as to whether the powertrain is in the lash zone or whetherthe lash is complete. If it is determined at step 80 that the lash isnot completed and the powertrain is not in the lash zone, then themethod loops back to step 70, which is the same as when there is anegative result at decision block 76. If, however, at decision block 80it is determined that the powertrain has either completed the lash or isstill in the lash zone, then the method moves onto the zone 3 controllabeled “B” in FIG. 3 and described in detail in conjunction with FIG.6.

Returning to step 78 and FIG. 3, a determination is made as to adaptiontorque levels and adaption torque durations for the first controlstrategy in zone 1. As part of this determination, a number of inputsmay be used, for example: whether the powertrain is still in the lashzone or whether lash is complete, the current torque request level, thecurrent transmission gear, information regarding the road grade, thedriveline temperature, and the torque converter state. Other inputs maybe used or fewer of these inputs may be used, as desired to modify thedetermination of the adaption levels. In general, if the duration of thefirst control strategy completes without the powertrain entering thelash zone, the method moves to implement the second control strategy forzone 2. If, however, lash is entered before completion of the zone 1control strategy, this control strategy is modified—i.e. adapted—to tryto ensure that in the next iteration the zone 1 control strategy willcomplete before lash is entered.

FIG. 4A shows a lookup table 82 with adaption levels for modifying thetorque request level implemented by the zone 1 strategy. As noted abovewith regard to the inputs for step 78, a great number of inputs may beconsidered when determining the adaption levels. For the lookup table82, the values are based on a particular driveline temperature, aparticular transmission gear, and the torque converter being in an openstate. Thus, use of the table 82 is based on the values of the inputsreceived at step 78. As shown in FIG. 4A, for the current torquelevel—i.e. the torque level applied in the zone 1 strategy at step70—and the current vehicle speed, a positive or negative adaptive torquevalue in Newton meters is determined. This adaptive torque value is thenused to modify the zone 1 control strategy, for example, at step 68 sothat in the next iteration of the zone 1 control strategy the torquerequest will be controlled with a modified version of the controlstrategy after another occurrence of a backlash predictor and beforeanother occurrence of backlash.

In addition to modifying the torque request level of the zone 1 controlstrategy, the duration of the zone 1 control strategy can also bemodified using the adaptive control strategy described herein. FIG. 4Bshows another lookup table 84, the use of which is also based onparticular levels of driveline temperature, transmission gear and torqueconverter state. Similar to the table 82, the table 84 may also be usedto make the determination described in conjunction with step 78 shown inFIG. 3. With regard to the table 84, current torque values used by thezone 1 control strategy and current vehicle speed are used to determinea modifier for the duration of the zone 1 control strategy the next timeit is implemented. As shown in FIG. 4B, the lookup table 84 includespositive and negative values of time (in seconds) that can be applied tothe duration of the zone 1 control strategy, for example, at step 68 asshown in FIG. 3.

Although step 78 in FIG. 3 describes determining adaption levels fortorque levels and durations of the zone 1 control strategy, differentimplementations may adapt only torque, only the duration, or both inorder to modify the zone 1 control strategy. For example, using thelookup table 84, a duration of the zone 1 control strategy may beincreased or reduced; this may be the extent of the modification to thezone 1 control strategy. Alternatively, using the lookup table 82, thezone 1 control strategy may be modified such that before adaption itincreases the filtered torque request to a first predetermined level,but after adaption, the first predetermined level is increased orreduced. In yet another implementation, the zone 1 control strategy maybe adapted by increasing or reducing its duration and also increasing orreducing the first predetermined level of the torque request.

As noted above, if the zone 1 control strategy completes itsduration—see step 72 in FIG. 3—the method moves on to a second controlstrategy—i.e., the zone 2 control strategy illustrated in the flowchart86 in FIG. 5. The second control strategy is implemented after the firstcontrol strategy and before the occurrence of backlash—i.e., it isimplemented after the zone 1 control, assuming that the lash zone wasnot entered during zone 1. Similar to step 68 and the first controlstrategy, a determination is made at step 88 as to what the desiredtorque level for the zone 2 control will be. The same or similar inputsmay be used to make this determination as were used in the determinationat step 68 for the zone 1 control—i.e., driveline temperature, a currentgear of the transmission, the road grade, and the driver requestedtorque, or others. The zone 2 torque request may be obtained, forexample, by determining the maximum twist speed for each gear andvehicle speed that will still allow the twist speed from upcoming zone 3to be achieved following the start of lash.

Once the determination is made at step 88, the torque request level isapplied during zone 2 as shown in step 90—this corresponds to the torquerequest level being reduced and moving from points 57, 57′ to the points59, 59′ as shown in the diagrams 50, 56, respectively. As shown in FIGS.2A and 2B, the torque request level at zone 2 is below the highesttorque request level obtained during the first control strategy of zone1. Similar to the zone 1 strategy, the zone 2 control strategy holds thetorque request constant throughout the duration of zone 2 if theconverter or other downstream clutch is open, such as shown in thediagram 50; conversely, the torque request level is increased throughoutthe zone 2 strategy if the converter or downstream clutch is locked,such as shown in the diagram 56. The rate of increase in the torquerequest level throughout zone 2—from the point 59′ to the point 61′—maybe determined as described above with regard to the rate of increase forzone 1, although other ways of determining this rate may be used.

As described above, the inputs received at step 88 will be used todetermine the zone 2 torque request level, but in general the torquerequest level will be reduced after zone 1 and before the lash zone isentered so that once the lash zone is entered, it will be easier toprovide a smooth transition through the backlash region. If the torquerequest was to remain at the level at the end of zone 1, indicated bythe points 57, 57′, it may be difficult to control the powertrainthrough the lash region without undesirable driveline disturbancesoccurring. To continue the example provided above, if the zone 1 maximumtorque request level is 20 Nm, it may be reduced at the start of thezone 2 control to a level of approximately 10 Nm.

After the torque request level is applied at step 90 in the flow chart86 shown in FIG. 5, the method moves to step 92 where a calculation ofthe duration of the zone 2 control strategy is made. During the firstiteration or application of the zone 2 control strategy, this time maybe based on the various inputs received at step 88, with a desired goalof completing the zone 2 control just as the lash zone is entered. Forfurther iterations of this step 92, the same inputs may be considered,but adaptive values may be applied to modify it from the firstiteration. After the zone 2 time is determined at step 92, the methodmoves to step 94, where determination is made as to whether certainadaption enable conditions are met. These may be, for example, the sameconditions that were used in step 74 illustrated in FIG. 3 and describedin detail above; however, they may consist of different combinations ordifferent conditions entirely as desired.

If the determination is made at decision block 94 that the adaptionenable conditions are not met, the method moves to step 96, wheredetermination is made as to whether the lash is already completed. If itis, the control strategy moves to the zone 4 strategy labeled “C” anddescribed in detail in conjunction with FIG. 7. If it is determined atdecision block 96 that the lash is not complete, the control strategymoves to step 98 where it is determined whether the zone 2 time hascompleted. If it has, the strategy then moves to the zone 3 strategy,labeled “B” and described in detail below in conjunction with FIG. 6.If, however, the zone 2 control strategy has not reached its time limit,a determination is made at step 100 as to whether the powertrain iscurrently in the lash zone. If it is, the strategy again moves to thezone 3 control strategy, but if it is not, the strategy loops back tostep 92 and repeats the subsequent steps.

Returning to step 94, if it is determined that the adaption enableconditions are met, the strategy moves to step 102 where a determinationis made as to whether lash is already complete. If it is not, thestrategy moves to step 104 where a determination is made as to whetherthe zone 2 control strategy has reached its time limit, and if not, thestrategy moves to step 106 where determination is made as to whether thepowertrain is currently in the lash zone. If it is determined at step106 that the powertrain is not in the lash zone, the control strategyloops back to step 92 and repeats the subsequent steps. If any of thethree steps 102, 104, 106 yields a positive result, the strategy movesto step 108 where the zone 2 adaption torque levels are determined.

Although step 108 only includes torque level adaption, other embodimentsmay include both torque level and duration adaption similar to step 78shown in FIG. 3. In addition, because both zone 1 and zone 2 controlstrategies have been implemented, the adaptions determined at step 108may include either or both of the zone 1 and zone 2 strategies. Thus, infuture iterations of the zone 1, zone 2, or both control strategies, amodified version of the applicable control strategy or strategies may beimplemented after the adaption levels are determined. The inputs for thedeterminations made at step 108 may be the same or similar to the inputsused at step 78 in FIG. 3 used for the zone 1 adaption strategy. Asshown in the flowchart 86, if step 108 was entered after step 102—i.e.,if the lash is already complete—the strategy moves on to the zone 4control strategy labeled “C” and described in detail in conjunction withFIG. 7. If step 108 was entered after either step 104 or 106, thestrategy moves to the zone 3 strategy, labeled “B” and described indetail in conjunction with FIG. 6. The specific adaption levelsdetermined at step 108—whether torque, duration, or both, may beretrieved from lookup tables, such as the lookup tables 82, 84 describedabove in conjunction with the zone 1 control strategy.

Turning to FIG. 6, a flowchart 110 illustrating a third control strategyis shown. The third control strategy is implemented after the occurrenceof backlash and before the backlash is complete. Similar to step 68 andthe first control strategy, a determination is made at step 112 as towhat the desired torque level for the zone 3 control will be. The sameor similar inputs may be used to make this determination as were used inthe determination at step 68 for the zone 1 control—i.e., drivelinetemperature, a current gear of the transmission, the road grade, and thedriver requested torque, or others. In at least some embodiments, thezone 3 torque request may be obtained by determining the maximum twistspeed for each gear and vehicle speed that produces an acceptable NVHlevel at the completion of lash. Once the determination is made at step112, the torque request level is applied during zone 3 as shown in step114—this corresponds to the torque request level being reduced andmoving from points 61, 61′ to the points 63, 63′ as shown in thediagrams 50, 56, respectively. As shown in FIGS. 2A and 2B, the torquerequest level at zone 3 is below the highest torque request levelobtained during the second control strategy of zone 2.

Similar to the zone 1 and zone 2 strategies, the zone 3 control strategyholds the torque request constant throughout the duration of zone 2 ifthe converter or other downstream clutch is open, such as shown in thediagram 50; conversely, the torque request level is increased throughoutthe zone 3 strategy if the converter or downstream clutch is locked,such as shown in the diagram 56. The rate of torque request levelincrease may be, for example, determined for zone 3 as it was describedabove for zone and 1 or zone 2. As described above, the inputs receivedat step 112 will be used to determine the zone 3 torque request level,but in general the torque request level will be reduced when the lashzone is entered. To continue the example provided above, if the zone 1maximum torque request level is 20 Nm, and the maximum torque requestlevel is 10 Nm in zone 2, the torque request level may be reduced at thestart of the zone 3 control to a level of approximately 5 Nm.

After the torque request level is applied at step 114 in the flow chart110 shown in FIG. 6, the method moves to step 116 where a calculation ofthe duration of the zone 3 control strategy is made. During the firstiteration or application of the zone 3 control strategy, this time maybe based on the various inputs received at step 112, with a desired goalof completing the zone 3 control just as the lash zone is completed. Forfurther iterations of this step 116, the same inputs may be considered,but adaptive values may be applied to modify it from the firstiteration. After the zone 3 time is determined at step 116, the methodmoves to step 118, where determination is made as to whether certainadaption enable conditions are met. These may be, for example, the sameconditions that were used in step 74 illustrated in FIG. 3 and describedin detail above; however, they may consist of different combinations ordifferent conditions entirely as desired.

If the adaption enable conditions are not met, the method goes to step120, where it is determined whether or not the zone 3 time limit hasbeen exceeded. As described above, it may be desirable to traverse thelash zone in a predetermined time period and it is determined at step120 whether this condition has been met. If it has, the strategy thenmoves to the zone 4 control strategy, labeled “C” and described indetail in conjunction with FIG. 7. If the time limit has not beenexceeded, the zone 3 control strategy moves to step 122, where adetermination is made as to whether the lash has already been completed.If it has not, the method loops back to step 118 to look at the adaptionenable conditions again. If it is determined at step 122 that the lashis complete, the strategy again moves to the zone 4 control strategydescribed in FIG. 7.

Returning to step 118 in the flowchart 110, if it is determined that theadaption enable conditions are met, the strategy moves to step 124 wherea determination is made as to whether lash is complete or the zone 3control strategy has reached its time limit. If the answer to both ofthese two inquiries is negative, the method loops back to the decisionblock at 118 where the adaption enable conditions are again reviewed. Ifeither of these inquiries is answered in the positive, the strategymoves to step 126 where the zone 3 adaption torque levels aredetermined.

Although step 126 only includes torque level adaption, other embodimentsmay include both torque level and duration adaption similar to step 78shown in FIG. 3. In addition, because control strategies for zone 1,zone 2 and zone 3 have been implemented, the adaptions determined atstep 126 may include a single one of any one of the three controlstrategies, or any combination of two or more of them. Thus, in futureiterations of the zone 1, zone 2 or zone 3 control strategy, or anycombination of two or more of them, a modified version of the applicablecontrol strategy or strategies may be implemented after the adaptionlevels in the zone 3 control are determined. The inputs for thedeterminations made at step 126 may be the same or similar to the inputsused at step 78 in FIG. 3 used for the zone 1 adaption strategy. Thespecific adaption levels determined at step 126—whether torque,duration, or both, may be retrieved from lookup tables, such as thelookup tables 82, 84 described above in conjunction with the zone 1control strategy. Once the adaption levels are determined, the zone 3control strategy may be modified so that on future implementations themodified control strategy is implemented. After the adaption levels aredetermined at step 126, the strategy moves to the zone 4 controlstrategy illustrated in FIG. 7.

A fourth control strategy is implemented in zone 4 after backlash iscomplete. A flowchart 128 shown in FIG. 7 illustrates one implementationof such a control strategy. At step 130, a determination is made as tohow to blend-in the requested torque profile. Specifically, the backlashcontrol strategies are now ending and standard powertrain control isreturning. A number of inputs may be used to make this determination,for example the same or similar inputs as were used in the determinationat step 68 for the zone 1 control. One way to determine how to blend-inthe requested torque is to increase the filtered torque request comingfrom the zone 3 control to reach the actual torque request level withina predetermined time period. This predetermined time period may be, forexample, the time period of one resonant frequency, which can be basedon, for example, the transmission gear and the natural frequency of thedriveline. Once the desired torque profile is determined at step 130,the zone 4 control strategy moves to step 132 where the torque profileis applied. At decision block 134 it is determined whether the currenttorque is equal to the requested torque, and if not, the method loopsback to step 132. If, however, it is determined at step 134 that thecurrent torque does equal the requested torque, then powertrain controlis returned to a standard control strategy and the backlash controlstrategy is ended.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A method for controlling backlash in a vehiclepowertrain, comprising: controlling a torque request of the powertrainwith a first control strategy after an occurrence of a backlashpredictor and prior to an occurrence of backlash; modifying the firstcontrol strategy when backlash occurs during the first control strategy;and controlling the torque request with the modified first controlstrategy after another occurrence of a backlash predictor and beforeanother occurrence of backlash.
 2. The method of claim 1, whereinmodifying the first control strategy includes reducing a duration of thefirst control strategy.
 3. The method of claim 2, wherein the firstcontrol strategy includes increasing the torque request to a firstpredetermined level, and modifying the first control strategy furtherincludes reducing the first predetermined level when the duration of thefirst control strategy is reduced to a first predetermined duration. 4.The method of claim 1, further comprising controlling the torque requestwith a second control strategy after the first control strategy andbefore the occurrence of backlash such that a torque request level isbelow a highest torque request level obtained during the first controlstrategy; modifying the second control strategy when backlash occursduring the second control strategy; and controlling the torque requestwith the modified second control strategy after another controlling ofthe torque request with the first control strategy and before anotheroccurrence of backlash.
 5. The method of claim 4, wherein modifying thesecond control strategy includes at least one of modifying a duration ofthe second control strategy or modifying a duration of the first controlstrategy.
 6. The method of claim 4, wherein modifying the second controlstrategy includes at least one of modifying a maximum torque level ofthe second control strategy or modifying the maximum torque level of thefirst control strategy.
 7. The method of claim 4, further comprising:controlling the torque request with a third control strategy after theoccurrence of backlash and before the backlash is complete such that atorque request level is below a highest torque request level obtainedduring the second control strategy; modifying the third control strategywhen a time to complete the backlash is outside a predetermined timeperiod; and controlling the torque request with the modified thirdcontrol strategy after another occurrence of backlash and before theother occurrence of backlash is complete.
 8. The method of claim 7,wherein modifying the third control strategy includes at least one ofmodifying a duration of the second control strategy or modifying aduration of the first control strategy.
 9. The method of claim 7,wherein modifying the third control strategy includes at least one ofmodifying a maximum torque level of the second control strategy ormodifying a maximum torque level of the first control strategy.
 10. Themethod of claim 7, further comprising controlling the torque requestwith a fourth control strategy after the backlash is complete such thatthe torque request is increased to an actual torque request level withina predetermined time period.
 11. A method for controlling backlash in avehicle powertrain, comprising: reducing at least one of a duration or amaximum torque level of a first control strategy for controlling atorque request of the powertrain when the first control strategy isimplemented after an occurrence of a backlash predictor and before anoccurrence of backlash, and backlash occurs before completion of thefirst control strategy.
 12. The method of claim 11, further comprisingreducing at least one of a duration or a maximum torque level of asecond control strategy for controlling the torque request when thesecond control strategy is implemented after the first control strategy,and backlash occurs before completion of the second control strategy.13. The method of claim 12, further comprising reducing at least one ofa duration or a maximum torque level of the first control strategy whenthe second control strategy is implemented after the first controlstrategy, and backlash occurs before completion of the second controlstrategy.
 14. The method of claim 12, further comprising reducing atleast one of a duration or a maximum torque level of a third controlstrategy for controlling the torque request when the third controlstrategy is implemented after the occurrence of backlash, and a time tocomplete the backlash is outside a predetermined time period.
 15. Themethod of claim 14, further comprising reducing at least one of aduration or a maximum torque level of the second control strategy whenthe third control strategy is implemented after the occurrence ofbacklash, and the time to complete the backlash is outside thepredetermined time period.
 16. A system for controlling backlash in avehicle powertrain, comprising: a control system, including at least onecontroller, configured to implement a first control strategy for atorque request after an occurrence of a backlash predictor and beforeoccurrence of a backlash, modify the first control strategy whenbacklash occurs during the first control strategy, and implement themodified first control strategy after another occurrence of a backlashpredictor and before another occurrence of backlash.
 17. The system ofclaim 16, wherein the control system is further configured to modify thefirst control strategy by at least one of modifying a duration of thefirst control strategy or modifying a maximum torque level of the firstcontrol strategy.
 18. The system of claim 16, wherein the control systemis further configured to implement a second control strategy for thetorque request after the first control strategy and before theoccurrence of backlash, and to modify the second control strategy whenbacklash occurs during the second control strategy by at least one ofmodifying a duration of the first control strategy or the second controlstrategy, or modifying a maximum torque level of the first controlstrategy or the second control strategy.
 19. The system of claim 18,wherein the control system is further configured to implement a thirdcontrol strategy for the torque request after the occurrence of backlashand before the backlash is complete, and to modify the third controlstrategy when a time to complete the backlash is outside a firstpredetermined time period by at least one of modifying a duration of thesecond control strategy or the third control strategy, or modifying amaximum torque level of the second control strategy or the third controlstrategy.
 20. The system of claim 19, wherein the control system isfurther configured to implement a fourth control strategy for the torquerequest after the backlash is complete such that the torque request isincreased to an actual torque request level within a secondpredetermined time period.